1. Field of Invention
The present invention relates to the directional placement of conductor pipe through some stratum or medium from an offshore platform. More particularly, the present invention relates to the directional placement of conductor strings or pipes at a desired curve and orientation from the vertical using deviated sections to facilitate the driving of the pipe or conductor string at desired and different orientations by preventing or by regulating the twist of the casing as it is hammered into the desired stratum during placement.
2. Prior Art
There are several possible uses for driving pipes at angles which vary in a deviated, off-the-vertical direction as they are driven through a stratum. This application is addressed specifically to the deviated placement of conductor casing for purposes of directional well drilling and/or dispersement of conductors on a multi-well platform to prevent conflict between conductor casings.
The need for directional drilling for oil and gas exploration and development is well known and several techniques exist for this purpose, as shown for example in U.S. Pat. No. Re. 29,929, reissued Mar. 13, 1979, and its predecessor U.S. Pat. No. 4,276,942, issued June 7, 1977, and the patents discussed and cited therein.
The idea of attempting to prevent a twist in a conductor string while it was driven down to prevent changes in direction from a desired path as the conductor string was implaced was partially considered in U.S. Pat. Nos. 4,276,943 and Re. 29,929, patents owned by the assignee hereof. Further, the use of outer, longitudinally directed "stabilizer bars" on the conductor itself at its entry end to react with the surrounding soil was recognized as being adapted to this use in those same patents.
This technique did act to prevent some twisting of the pipe but previously was only available at the point where the guiding "dog leg" section located at the front of the casing was in engagement with the soil. This technique has not been found to be one hundred percent effective, particularly when certain strata are encountered in the casing driving process, where some twisting of the casing was not adequately prevented.
The present invention is aimed at improving on the previous techniques and in minimizing this twist or controlling the twist for the purpose of controlling and further directing the horizontal deviation produced in the driving of deviated conductor casing.
3. General, Summary Discussion of the Invention
The present invention is applicable to the placement of deviated conductors from an offshore platform.
The invention utilizes in one embodiment a modified conductor guide or guides and conductor casing which use sets of longitudinally directed, mating, interdigitating, anti-twist bars modified to control the placement of the angular deviation of the casing as it is hammered into place. The conductor guide(s) are equipped along their internal diameter with jutting nodes or bars. Likewise, the outside of some of the conductor casing sections are similarly equipped with jutting, longitudinally directed bars.
The outside diameter of the conductor casing is sufficiently small so that the conductor casing can fit through and be guided by the conductor guide(s) despite the presence of the anti-twist bars on the inside of the conductor guides and on the outside circumference of the casing sections. However, the diameters of the conductor guide(s) and the conductor casing are sufficiently close so that the bars on the conductor guide(s) will contact the sides of the anti-twist bars on the casing sections if the casing attempts to twist away from its set direction as it is driven into the stratum. The opposing, anti-twist bars by way of this contact at least substantially prevent any undesired twisting of the conductor casing along the casing's longitudinal axis.
Although the anti-twist bars or "stops" which arrest the twist of the casing are referred to as "bars" throughout this specification, it should be recognized that the shape and form of the "stops" as well as the elemental makeup of the "stops" may be varied as is structually and functionally desirable, for example to make them in a more resilient manufacture or to cause the pipe to move more downwardly or upwardly by the relative shape of the bars, without departing from the basic concept of the invention disclosed herein.
For reasons which will become apparent, it may be desired that the speed with which the casing twists before being arrested is either increased or decreased prior to being arrested. For this purpose, a cable or chain (or other band, wheel or roller) and winch apparatus is provided in a second embodiment, so that the motion of the casing along its longitudinal axis is either increased or decreased as it is driven downwardly by the driving hammer. This cable or chain (of other band, wheel or roller) is made to contact the pipe by wrapping the cable or chain (or other band, wheel or roller) around the outer diameter of the casing or by otherwise contacting the casing. The cable or chain (or other band, wheel or roller) may be made to twist with or against the twisting of the pipe, so as to increase or slow down the pipe's movement along its longitudinal axis (the twist of the pipe) by winding the chain, etc. in one direction or the other as it is wrapped around or pressed against the pipe. Primarily, this "wrapping" technique could be used as an independent control system regardless of any interdigitating "bar" anti-twist system on the guide(s) and conductor casing sections.
The utility of this invention is that, when the undesired "twist" movement of the pipe is minimized or arrested, the improper placement of the deviation is avoided, as the conductor sections are driven into the stratum where the casing is to be placed. The present invention thus is useful for minimizing improper or undesired horizontal deviations or giving greater control to the desired deviation and to the amount and direction of deviation.
Because the twist may be such as to crack or break structures, such as the bars used in this invention, due to the great forces which can be developed, the invention also provides for the design of cable or chain and winch arrangements to minimize the twist prior to the bars being contacted.
The present invention may be used in concert with one of the other deviation systems such as slanted or jutting dog legs and other attaching direction slanting devices or systems known in the art.